$num: 4;
$x: 10px;
$y: 20px;
div {
  font-size: 10px * $num;
  // font-size: (10px / $num);
  border-width: 3px + 2px;
  padding: 10px - 2px;
  margin: (100px - $x) / $num * 3;
}
